The present invention relates to monitoring apparatus for monitoring the operation of electronic equipment having n circuits to be monitored, each circuit having its own fault-detection means with a flag output terminal capable of indicating a fault in the circuit. The apparatus comprises fault indicating means connected to the terminals for indicating the presence of a fault on any of the terminals, and fault-simulation means for simulating faults which, in fault-simulating operation, cyclically put the terminals into the fault condition.
The invention is applicable to electronic equipment such as the time-base for a computer or a digital switching exchange, that is required to operate very securely. For this purpose, such equipment is often redundantly designed and supplies an output signal which is taken from a majority vote of a number of identical units. Further, it is necessary to monitor the operation of the different units continuously and repetitively in order to ensure that faulty units do not excessively reduce the degree of redundancy.
It is known, as mentioned above, to provide the various circuits which constitute the electronic equipment to be monitored with respective fault-detection means. These fault-detection means may, for example, be logical comparators which, in a redundant structure, are connected to compare the output of a circuit with the associated majority signal output. When there is a difference between the compared signals, the fault-detection means indicate a fault, and may optionally indicate the location of the fault (localization).
To monitor the fault-detection means it is necessary to simulate faults. It is thus necessary to deliberately produce faults and then to analyze the response of the fault-detection means and of the fault indicating means.
Apparatus which only simulates n faults (one per circuit to be monitored) can only provide partial monitoring of the overall fault detection and gathering system.